Attention is directed to commonly assigned copendinq application: (D/A0890) filed concurrently herewith, entitled xe2x80x9cELECTROSTATOGRAPHIC IMAGING MEMBERxe2x80x9d which discloses a process including providing at least a flexible substrate layer having a first major surface on one side and a second major surface on a second side opposite the first major surface, the first major surface being an exposed surface, applying a coating of an anti-curl backing layer dispersion on the first major surface of the substrate layer, the dispersion comprising a volatile carrier liquid, a film forming polymer dissolved in the volatile carrier liquid, a film forming polymer dissolved in the volatile carrier liquid, solid organic particles dispersed in the volatile carrier liquid, and an organic additive, such as a fluorinated acrylate copolymer, dissolved in the volatile carrier liquid; and drying the coating to remove the volatile carrier and form a dried anti-curl backing layer. An electrostatographic imaging member containing the resulting anti-curl backing layer is also described.
The disclosures of the above mentioned copending application is incorporated herein by reference in its entirety. The appropriate components and processes of these patents may be selected for the articles and processes of the present invention in embodiments thereof.
The present invention relates to an imaging member fabrication process and, more specifically, to a process for fabricating anticurl backing layers for flexible electrostatographic imaging members.
Electrostatographic flexible imaging members are well known in the art. Typical electrostatographic flexible imaging members include, for example, photosensitive members (photoreceptors) commonly utilized in electrophotographic (xerographic) processes and electroreceptors such as ionographic imaging members for electrographic imaging systems. The flexible electrostatographic imaging members may be seamless or seamed belts. Typical electrophotographic imaging member belts comprise a charge transport layer and a charge generating layer on one side of a supporting substrate layer and an anticurl backing layer coated on the opposite side of the substrate layer. A typical electrographic imaging member belt comprises a dielectric imaging layer on one side of a supporting substrate and an anticurl backing layer on the opposite side of the substrate.
Electrophotographic flexible imaging members may comprise a photoconductive layer comprising a single layer or composite layers. One type of composite photoconductive layer used in electrophotography is illustrated in U.S. Pat. No. 4,265,990 which describes a photosensitive member having at least two electrically operative layers. One layer comprises a photoconductive layer which is capable of photogenerating holes and injecting the photogenerated holes into a contiguous charge transport layer. Generally, where the two electrically operative layers are supported on a conductive layer with the photoconductive layer sandwiched between the contiguous charge transport layer and the conductive layer, the outer surface of the charge transport layer is normally charged with a uniform charge of a negative polarity and the supporting electrode is utilized as an anode. Obviously, the supporting electrode may still function as an anode when the charge transport layer is sandwiched between the supporting electrode and the photoconductive layer. The charge transport layer in this latter embodiment must be capable of supporting the injection of photogenerated electrons from the photoconductive layer and transporting the electrons through the charge transport layer. Photosensitive members having at least two electrically operative layers, as disclosed above, provide excellent electrostatic latent images when charged with a uniform negative electrostatic charge, exposed to a light image and thereafter developed with finely divided electroscopic marking particles. The resulting toner image is usually transferred to a suitable receiving member such as paper.
As more advanced, higher speed electrophotographic copiers, duplicators and printers were developed, degradation of image quality was encountered during extended cycling. Moreover, complex, highly sophisticated duplicating and printing systems operating at very high speeds have placed stringent requirements including narrow operating limits on photoreceptors. For electrophotographic imaging members having a belt configuration, the numerous layers found in modern photoconductive imaging members must be highly flexible, adhere well to adjacent layers, and exhibit predictable electrical characteristics within narrow operating limits to provide excellent toner images over many thousands of cycles. One type of multilayered photoreceptor that has been employed as a belt in electrophotographic imaging systems comprises a substrate, a conductive layer, a blocking layer, an adhesive layer, a charge generating layer, a charge transport layer, and a conductive ground strip layer adjacent to one edge of the imaging layers. This photoreceptor belt may also comprise additional layers such as an anticurl backing layer to achieve the desired belt flatness. An optional overcoating layer over the charge transport layer may be used for wear and chemical protection.
In a machine service environment, a flexible imaging member belt, mounted on a belt supporting module, is generally exposed to repetitive electrophotographic image cycling which subjects the exposed anticurl backing layer to abrasion due to mechanical fatigue and interaction with the belt drives and other support rollers as well as sliding contact with backer bars. This repetitive cycling leads to a gradual deterioration in the physical/mechanical integrity of the exposed anticurl backing layer. When the anticurl layer is worn the thickness thereof is reduced and the anticurl backing layer experiences a loss of ability to counteract the tendency of imaging members to curl upwardly thereby leading, to belt curl. Moreover, uneven wear of the anticurl backing layer has been found to cause early development of belt ripples which are ultimately manifested as copy printout defects. Thus, the anticurl backing layer wear resulting from mechanical contact interaction during dynamic imaging operations is a serious problem that shortens the service life of the belt and adversely affects image quality.
When a production web stock of several thousand feet of coated multilayered photoreceptor is rolled up, the charge transport layer and the anticurl layer are in intimate contact. The high surface contact friction of the charge transport layer against the anticurl layer causes dimples and creases to develop in the internal layers of the photoreceptor. Since these physically induced defects manifest themselves as print defects in xerographic copies, the unacceptable segments of this photoreceptor web stock are discarded thereby decreasing production yield. Although attempts have been made to overcome these problems, the solution of one problem often leads to the generation of additional problems.
Flexible photoreceptor belts are fabricated from sheets cut from an electrophotographic imaging member web stock. The cut sheets are generally rectangular in shape. All edges may be of the same length or one pair of parallel edges may be longer than the other pair of parallel edges. The sheet is formed into a belt by joining the overlapping opposite marginal end regions of the sheet. A seam is typically produced in the overlapping opposite marginal end regions at the point of joining. Joining may be effected by any suitable means such as welding (including ultrasonic processes), gluing, taping, pressure/heat fusing, and the like. However, ultrasonic seam welding is generally the preferred method of joining because it is rapid, clean (no application of solvents) and produces a thin and narrow seam. The ultrasonic seam welding process involves a mechanical pounding action of a welding horn which generate a sufficient amount of heat energy at the contiguous overlapping marginal end regions of the imaging member sheet to maximize melting of one or more layers therein. A typical ultrasonic welding process is carried out by holding down the overlapping ends of the flexible imaging member sheet with vacuum onto a flat anvil and guiding the flat end of the ultrasonic vibrating horn transversely across the width of the sheet and directly over the overlapped junction to form a welded seam having two adjacent seam splashings consisting of the molten mass of the imaging member layers ejected to the either side of the welded overlapped seam. These seam splashings of the ejected molten mass comprise about 40 percent by weight of anticurl layer material. The splashings can include hard crystalline materials and have a rough abrasive outer surface which abrades the photoreceptor cleaning blade during dynamic image cycling causing the blade to lose cleaning efficiency and shortens blade service life.
Alteration of material formulation in the anticurl backing layer of imaging member belt can enhance wear resistance and extend life, but this can also produce undesirable outcomes For example, incorporation of crystalline particles in the outermost exposed layers of the imaging member to improve wear resistance has been observed to cause excessive wear of the ultrasonic horn used to ultrasonically weld the seams of imaging belts. Thus, the resolution of one problem has led to the creation of another problem. In another prior art approach to resolve the imaging member coating layer wear problems, synthetic organic particles have been incorporated into the exposed anticurl backing layer of the imaging member to improve abrasion resistance. However, such incorporation has been observed to cause the formation of bubbles in the dried anticurl backing layer. These bubbles adversely affect the thickness uniformity of the layer which in turn affects critical physical characteristics such as, for example, alteration of intimate surface contact friction requirements between the anticurl backing layer and the drive-roller of the belt support module. This alteration of friction adversely impacts the driving capacity of drive-rollers thereby causing imaging belt slippage during dynamic belt operation. Moreover, the alteration has also been found to reduce the mechanical strength of anticurl backing layers and capability to resist fatigue induced anticurl backing layer cracking. The presence of bubbles in the anticurl backing layer can also negate and diminish the benefit of wear resistance enhancements, otherwise achievable through dispersion of organic particles in imaging members, by increasing wear rate. Also, due to the presence of bubbles, weakening of the layer and premature cracking of the imaging member can occur when fatigue tension/compression strain is repeatedly applied to the anticurl backing layer during machine cycling, particularly when cycling around small diameter support rollers. Further, when rear erase is employed to discharge the photoreceptor belt during electrophotographic imaging processes, the presence of bubbles causes a light scattering effect which leads to undesirable non-uniform discharge. Also, the presence of bubbles in the anticurl backing layer during seam welding processes cause the bubbles to expand and form splashings having open pits. During electrophotographic imaging and cleaning cycles, these open pits can function as sites that trap toner, debris, and dirt particles making attempts to clean the imaging member belt extremely difficult. It has also been found that, during imaging belt cycling, the trapped toner, debris, and dirt particles can be carried out by the cleaning blade from the pits to contaminate the vital imaging components such as lenses, HSD, HJD and, other subsystems, and can also lead to undesirable artifacts which form undesirable printout defects in the final image copies.
U.S. Pat. No. 5,021,309 to R. Yu, issued Jun. 4, 1991xe2x80x94In an electrophotographic imaging device, material for an exposed anti-curl layer has organic fillers dispersed therein are disclosed The fillers provide coefficient of surface contact friction reduction, increased wear resistance, and improved adhesion of the anti-curl layer, without adversely affecting the optical and mechanical properties of the imaging member.
U.S. Pat. No. 5,096,795 to R. Yu, issued Mar. 17, 1992xe2x80x94An electrophotographic imaging device is disclosed in which material for exposed layers contain either organic or inorganic particles uniformly dispersed therein. The particles provide reduced coefficient of surface contact friction, increased wear resistance, durability against tensile cracking, and improved adhesion of the layers without adversely affecting the optical and electrical properties of the imaging member.
U.S. Pat. No. 5,725,983 to R. Yu, issued Mar. 10, 1998xe2x80x94An electrophotographic imaging member is disclosed comprising a supporting substrate having an electrically conductive layer, a hole blocking layer, an optional adhesive layer, a charge generating layer, a charge transport layer, an anticurl back coating, a ground strip layer and an optional overcoating layer, at least one of the charge transport layer, anticurl back coating, ground strip layer and overcoating layer comprising a blend of inorganic and organic particles homogeneously distributed in a weight ratio of between about 3:7 and about 7:3 in a film forming matrix, the inorganic particles and organic particles having a particle diameter less than about 4.5 micrometers. These electrophotographic imaging members may have a flexible belt form or rigid drum configuration. These imaging members may be utilized in an electrophotographic imaging process.
U.S. Pat. No. 4,647,521 to Y. Oguchi et al., issued Mar. 3, 1987xe2x80x94A photosensitive member or image holding member, for electrophotography is disclosed having a conductive substrate, a top layer for holding an electrostatic image and/or toner image wherein the top layer is formed by applying a coating fluid containing hydrophobic silicon and a binder resin.
U.S. Pat. No. 4,654,284 to R. Yu. et al., issued Mar. 31, 1987xe2x80x94An imaging member is disclosed comprising at least one flexible electrophotographic imaging layer, a flexible supporting substrate layer having an electrically conductive surface and an anticurl layer, the anticurl layer comprising a film forming binder, crystalline particles dispersed in the film forming binder and a reaction product of a bifunctional chemical coupling agent with both the film forming binder and the crystalline particles. This imaging member may be employed in an electrostatographic imaging process.
U.S. Pat. No. 4,664,995 to A. Horgan et al., issued May 12, 1987xe2x80x94An electrostatographic imaging member is disclosed comprising at least one imaging layer capable of retaining an electrostatic latent image, a supporting substrate layer having an electrically conductive surface, and an electrically conductive ground strip layer adjacent the electrostatographic imaging layer and in electrical contact with the electrically conductive layer, the electrically conductive ground strip layer comprising a film forming binder, conductive particles and crystalline particles dispersed in the film forming binder, and a reaction product of a bifunctional chemical coupling agent with both the film forming binder and the crystalline particles. This imaging member may be employed in an electrostatographic imaging process.
U.S. Pat. No. 4,869,982 to W. Murphy, issued Sept. 26, 1989xe2x80x94An electrophotographic photoreceptor is disclosed containing a toner release material in one or more electrically operative layers such as a charge transport layer. From about 0.5 to about 20 percent of a toner release agent selected from stearates, silicon oxides and fluorocarbons is incorporated into an imaging layer such as a charge transport layer.
U.S. Pat. No. 5,215,839 to R. Yu, issued Jun. 1, 1993xe2x80x94A layered electrophotographic imaging member is disclosed. The member is modified to reduce the effect of interference caused by the reflections from coherent light incident on a ground plane. Modification involves an interface layer between a blocking layer and a charge generation layer, the interface layer comprising a polymer having incorporated therein filler particles of a synthetic silica or mineral particles. The filler particles scatter the light to prevent reflections from the ground planes back to the light incident the surface.
U.S. Pat. No. 5,096,792 to Y. Simpson et al, issued Mar. 17,1992xe2x80x94A layered photosensitive imaging member is disclosed which is modified to reduce the effects of interference within the member caused by reflections from coherent light incident on a base ground plane. The modification involves a ground plane surface with a rough surface morphology by various selective deposition methods. Light reflected from the ground plane formed with the rough surface morphology is diffused through the bulk of the photosensitive layer breaking up the interference fringe patterns which are later manifested as a plywood pattern on output prints made from the exposed sensitive medium.
While the above mentioned electrophotographic imaging members may be suitable for their intended purposes, there continues to be a need for improved processes for fabricating imaging members, particularly for material modified multilayered electrophotographic imaging members having mechanically robust exposed layers in a flexible belt configuration.
It is therefore an object of the present invention to provide improved process for fabricating anticurl backing layers for layered electrostatographic imaging members which overcome the above noted disadvantages.
It is another object of the present invention to provide an improved process for fabricating anticurl backing layers that involve a modified anticurl layer coating composition.
It is also an object of the present invention to provide an improved process for fabricating anticurl backing layers that enhances optical clarity and superior lubrication characteristics of the anticurl backing layers.
It is yet another object of the present invention to provide an improved process for fabricating anticurl backing layers having the ability to suppress the development of belt ripples during dynamic imaging belt cycling.
It is still an object of the present invention to provide an improved process for fabricating anticurl backing layers for flexible layered electrostatographic imaging member belts involving the use of a reformulated anticurl backing layer coating composition that improves seam splashing surface lubrication.
It is a further object of the present invention to provide an improved process for fabricating anticurl backing layers that leads to improved flexible layered electrostatographic imaging belts having a seam splashing morphology that resists the early onset of fatigue bending induced seam cracking and delamination.
It is also another object of the present invention to provide an improved process for fabricating anticurl backing layers that are mechanically robust and provide clean machine belt cycling with minimum wear and generation of debris and dust.
It is another object of the present invention to provide an improved process for fabricating anticurl backing layers to produce an improved layered flexible electrophotographic imaging members web having reduced surface contact friction between the charge transport layer and the anticurl back coating in rolled up web stock.
It is still a further object of the present invention to provide an improved process for fabricating anticurl backing layers having organic particles dispersed in the which do not cause ultrasonic horn wear during the ultrasonic welding of seams to form belts.
It is yet another object of the present invention to provide an improved process for fabricating anticurl backing layers to form improved layered flexible electrophotographic imaging member belts that are free of belt wrinkles, puckering, and ripples that induce print copy output defects.
It is also an object of the present invention to provide an improved process for fabricating anticurl backing layers using a reformulated anticurl backing layer containing organic particles dispersion in a film forming polymer matrix which is free of bubble defects and which produces enhanced wear resistant anticurl backing layers in flexible electrostatographic imaging member belts.
These and other objects of the present invention are accomplished by a process comprising
providing at least a flexible substrate layer having a first major surface on one side and a second major surface on a second side opposite the first major surface, the first major surface being an exposed surface,
applying a coating of an anticurl backing layer dispersion on the first major surface of the substrate layer, the dispersion comprising
a volatile carrier liquid,
a film forming polymer dissolved in the volatile carrier liquid,
solid organic particles dispersed in the volatile carrier liquid, and
a dissolved organic additive represented by the structural formula: 
xe2x80x83dissolved in the volatile carrier liquid,
wherein
m is a number from 1 to 99,
n is a number from 1 to 99,
p is an integer between 1 and 10,
f is an integer between 1 and 8, and
I is an integer between 10 and 500, and
drying the coating to remove the volatile carrier and form a dried anticurl backing layer.
An electrostatic imaging member fabricated by the above-described process is also contemplated.
Although the discussions hereinafter will focus mainly on fabricating flexible electrophotographic imaging member belts (photoreceptor belts), they are equally applicable to fabricating electrographic imaging members (e.g., ionongraphic belts).
Flexible electrophotographic imaging member belts generally comprise a supporting substrate having an electrically conductive surface, an optional hole blocking layer, an optional adhesive layer, a charge generating layer, a charge transport layer, an anticurl backing layer, an optional ground strip layer and an optional overcoating layer. The exposed anticurl backing layer fabricated by the process of this invention comprises synthetic organic particles homogeneously dispersed in a film forming polymer matrix which overcomes the deficiencies of prior anticurl backing layers.